1. Field of the Invention
The present invention relates to an image encrypting method and device which decomposes original image data into a plurality of components and encrypts them, a method and device which decrypts an encrypted image file which has been obtained by this image encrypting method and device, and a computer readable recording medium which records a program to cause a computer to execute these methods.
2. Description of the Related Art
For some applications which handle image data of popular talents, particular characters, etc. having their portrait rights or the copyright, it is required to inhibit that the image data is used for any purpose other than a specific one. In other words, if such image data having the copyright can be freely reproduced with general computers, there is the possibility of that the portrait rights and the copyright are infringed, thus it is required that such image data be permitted to be printed out only by a particular authorized lab, and cannot be used for any other purposes.
Thus, a technique has been proposed which offers image data encrypted so that it can be decrypted only by the application software and the lab permitted to make printout. This technique is such that only the application software and a particular lab have the capability of decrypting encrypted image data, and the application software and the particular lab cannot output image data having the copyright, etc. for any purpose other than a particular one.
On the other hand, as a method for storing of image data, various methods, such as JPEG, GIF, and TIFF, are available, however, in recent years, the method has been proposed which hierarchically decomposes image data for the resolutions or density resolutions, and encodes the data for the hierarchical levels (the hierarchical data) to compress and store them. This storing method is such that it decomposes image data into hierarchical data for a plurality of resolutions or density resolutions by wavelet-conversion or other technique, and this decomposed data for the resolutions or density resolutions is encoded in the order of hierarchical levels to be compressed and stored as a file.
This storing method has the following features:    (1) Unlike the DCT method used with the prior art JPEG, the image data is not processed for each block, thus such an artifact as block distortion will not be caused.    (2) Because the image data is hierarchically encoded, only the information for the necessary resolution is required to be transferred in transferring the image data, thus efficient image transfer can be performed.    (3) Because the image data is decomposed for multiple resolutions or multiple density resolutions, a variety of image processes such as frequency emphasized processing can be performed relatively easily.    (4) Simultaneous spatial and frequency decomposition by multiple resolution analysis can be made, and for the low frequency region which has a great effect on the encoding efficiency, orthogonal transformation is performed in a wide range, while for the high frequency region, orthogonal transformation can be achieved in a narrow range, thus, if a quantization noise is generated around the edge in the image, the spatial spread can be suppressed. This makes the noise difficult to be perceived.
In addition, a file format which allows a plurality of data having different properties to be stored in a single file, as with the FlashPix file proposed by Eastman Kodak, has been proposed, and in such a file meeting the FlashPix specifications as this, hierarchical data decomposed for multiple resolutions or multiple density resolutions can also be stored.
Further, the methods which constitute an image file by, for example, decomposing the image data into a chromaticity signal and a luminance signal; decomposing it for the frequency components; decomposes it into a α-channel information representing the luminous transmittance of the image or into depth information representing the distances from the camera and RGB data; and decomposing the image into a plurality of blocks are used. In addition, for a plurality of images or a composite image obtained by composing an image with a template, the image file is constituted by data of each image, image layout information, character information, etc.
Thus, when an image file is constituted by a plurality of data (hereafter referred to as components), only particular components are encrypted in some cases. For example, when the image data has been hierarchized as stated above, only the hierarchical data having the highest resolution, which is the most valuable as image, is encrypted. With an image file wherewith only a part of the components has been encrypted, anyone can reproduce image data for the components which have not been encrypted, and the hierarchical data having the highest resolution which is suited for printout, etc. can be used only by a person having the decryption key for decrypting the encrypted hierarchical data. Therefore, any person other than the authorized person who has the right, having received the encryption key from the copyright holder for the image cannot use the image having the highest resolution, which allows prevention of illegal use of an image having the copyright, etc.
However, when a plurality of components of the components have been encrypted, it cannot be known that, by what encryption system, each component has been encrypted. Therefore, even the authorized person who has received the encryption key must try to decrypt all the encrypted components by use of that encryption key to know which component can be decrypted by the encryption key, thus the operation is extremely cumbersome. In addition, when an image file is to be brought into a lab to request printout, the user cannot know that the components required by him are to be brought into which lab for decryption, great confusion is produced in printout request.
The purpose of the present invention, which has been provided by taking the above-stated situation into consideration, is to offer an image encrypting method and device whereby, when a plurality of components of the components have been encrypted, the encrypted components can be decrypted without confusion; an image decrypting method and device; and a computer readable recording medium which records a program to cause a computer to execute these methods.